Cleaning furnace tube



April 13, 1937- c. L. JOHNSTON CLEANING FURNACE TUBE Filed July 10, I954INVENTOR CHAR S JOHNSTON BY ATTORNEY Patented Apr. 13, 1937 UNITEDSTATES. PATENT OFFICE CLEANING FURNACE TUBE Charles L. Johnston, LongBeach, Calif., assignor to Universal Oil Products Company, Chicago,111., a corporation of Delaware Application July 10, 1934, Serial No.734,523 teams. (01. 196-69) This invention particularly refers to animproved method for removing carbonaceous deposits from the interiorsurface of tubular elements in oil heaters which is particularly welladapted to use in furnaces for the distillation or pyrolytic conversionof hydrocarbon oils.

In all processes (either distillation or conver-' sion) whereinhydrocarbon oils of a relatively heavy nature are heated to hightemperatures in a fluid conduit there is a tendency for the coke toaccumulate upon the inner surface of the fluid conduit. This greatlyhinders the transmission of heat to the oil and may result in eventualstoppage or failure of the fluid 'conduit- 16 It is the purpose 'ofthe-present invention to keep the fluid conduits of oil heaters freefrom any excessive coke accumulation by periodically removing theaccumulated coke from the fluid conduit before there has been asufficient quan- 20 tity accumulated to greatly hinder the operation ofthe process, or to damage the conduit tubes due to overheating resultingfrom the excessive carbon deposits. If renewal or replacement of.damaged tubes is not made, eventually 25 a flre hazard will be created.This purpose is accomplished by controlled alternate cooling and Iheating of the fluid conduit by passing through the fluid conduit, orthrough that portion of the conduit wherein the coke accumulates, in the30 order named, a mixture of water and steam,

water, hot oil and cold oil, whereby to loosen the deposited coke fromthe walls of the fluid conduit and flush the loosened coke from thesystem.

While I have determined, within fairly close limits, the conditions mostsuitable for removing coke from the tubular elements of the fluidconduit following the processing of certain types of oils under specificconditions of treatment and will later outline these preferredconditions in more detail, I do not wish to be limited thereby since Ibelieve the best conditions of temperature, time of treatment, etc.,will vary depending 45 upon the nature of the coke deposit which, inturn, is related to the type of oil treated and theconditions oftreatment to which it is subjected. The success of the improved methodof the present invention is dependent, I believe, at

50 least in part, upon the provisions for cooling, heating and againcooling the tubes. I attribute this to the difference of the coeflicientof expansion between the metal Walls of the tube and the'carbonaceousdeposit accumulated therein, 55 the alternate contraction and expansionof the tubes serving to loosen the coke deposit so that it may beflushed from the tubes.

The invention is, therefore, in its broadest aspect, limited only toalternate cooling and. heating of the fluid conduit followed by flushingof 5 the carbonaceous material from the tubes. However, considerableimportance is attached to the particular steps employed in the presentinvention and their sequence, namely, the use of water and steamfollowed by the use of water 10 and then by the introduction of hot oiland finally by flushing of the tubes with cold oil, although due to thepossibility of obtaining fair results by slight modifications anddepartures from the preferred conditions, it is not intended to limitthe invention to the use of specific materials nor to a specificsequence of steps nor to the specific temperature conditions hereinaftermentioned.

The accompanying diagrammaticdrawing illustrates one specific form ofoil heating furnace with provisions for employing the features of thepresent invention and the following description of the drawing willserve to more clearly illustrate one adaptation of the process of thepresent invention.

Referring to the drawing, the furnace l comprises, in the caseillustrated, a combustion zone 2 and a heating zone 3. A combustiblefuel-air mixture is supplied to combustion zone 2 through suitablefiring ports 4 by means of any suitable form of burners, the tips ofwhich are indicated at 5. Combustion of the fuel is substantiallycompleted in zone Z'of the furnace and the hot combustion gases passthrough perforations B in the central wall I of the furnace 'intoheating zone 3, flowing downward therethrough over the tubular elements8 of fluid conduit 9, located within this zone, and passing thencethrough flue ill to a suitablestack, not shown. 40

Fluid conduit 9, in the case here illustrated, comprises a plurality ofsuperimposed horizontally parallel rows of horizontally disposed tubes 8extending between the end walls of the furnace and connected, asindicated, in series by means of suitable return bends i I. The returnbends on only the near end of the furnace are shown in the drawing. Inthe case here illustrated, the inlet to the heating coil is at thebottom of the tube bank on the near end of the furnace and the outlet isat the top of the tube bank on the far end of the furnace.

During normal operation of the process, oil may be supplied from anysuitable source through line l2 and valve 13 to pump M by means of whichit is fed through line l5 and valve Hi to the fluid conduit, flowingtherethrough in a general upward direction and being heated to thedesired temperature by the hot combustion 6 gases passing throughheating zone 3, the stream of heated oil being discharged from the upperportion of the tube bank through line I! and valve l8 to subsequentportions of the-oil treating process not pertinent to the presentinvention 10 and therefore not illustrated.

After an appreciable amount of coke has been i deposited upon the innerwalls of tubes 8 of the fluid conduit but before a sufilcient quantityof coke has accumulated thereon to greatly hinder l5 smooth operation ofthe process or to create a fire hazard, the supply of fuel to thecombustion zone of the furnace is discontinued so that the fires areextinguished and by opening valve is in drop-out line the oil ispermitted to drain from 20 the heating coil, pump I 4 having, of course,been stopped and valve I6 closed in order to discontinue the supply ofcharging stock to the heating coil.

Simultaneous with or following the opening of valve IS in line 20, valveIt, in line H, is closed and valves 22 and 24 in the respective lines 2|and 23 are opened, admitting steam and water,

through the respective lines and through lines 25 and I! to heating coil9, forcing out the oil through line 20 and reducing the temperature inthe heating coil. The quantity of steam admitted through line 2| isgradually diminished and the quantity of water admitted through line 23gradually increased until the temperature of the material leaving theheating coil has reached approximately 200 F., as measured, for example,at a point indicated by pyrometer 26 in line IS. The supply of steam tothe heating coil is then stopped by closing valve 22 and the flow ofwater through the heating coil is continued until the temperature of thewater leaving the heating coil is approximately 100 F., or less.

The supply of water is then shut off by closing valve 24, valve I9 isclosed and hot oil is charged 4 to the heating coil from any suitablesource such as, for example, by diverting a portion of the stream ofheated oil from a similar furnace, not illustrated, through line 21 andvalve 28 and through line I! into heating coil 9, the temperature of theoil being preferably in the neighborhood of 500 E, or thereabouts. Thewater may be allowed to drain from the heating coil through valve l0 andline 22, prior to the introduction of the heated oil, or the stream ofheated oil may be employed to force the water out of the heating coil,for example, through line 29 and valve 3. into tank 3|.

When desired, any or all of the materials above mentioned (water, steamand heated oil) may be supplied to the heating coil from the oppositedirection to that illustrated and above described by well known means,not illustrated. Also, when desired, any or all of the various materialsmay be supplied to and/or withdrawn from the heat-' ing coil at anydesired intermediate point or plurality of points therein. This may beaccomplished by connecting the supply lines to any one or more of thevarious return bends H and by discharging materials thus supplied to theheating coil from either the inlet or outlet end of the heating coil orfrom a suitable intermediate point beyond the point of introduction ofthe materials. This method of operation is particularly desirable incase an appreciable deposit of carbonaceous material occurs in only aportion of the heating coil, in which event it is not necessary to applythe cleaning method provided by the present invention to the relativelyclean portion of the heating coil.

After the heating coil has been charged with heated oil at a temperatureof about 500 F., pump it may be again started to supply relatively coldcharging stock to the heating coil, in the manner previously described.The flow of relatively cool oil to the heating coil is continued at arapid rate for a period of time (10 minutes, for example) in order toflush out the carbon in the tubes, the stream of oil and coke passingfrom the heating coil, for example, through line 29 and valve 30 intotank 3| wherein the coke may be allowed to -.settle out.

Following this operation the fires may be relighted in combustion zone 2and the normal operation of the process continued.

The conditions of operation above given in connection with thedescription of the drawing are those which have been found satisfactoryfor the removal of coke from the furnace tubes of a topping plantoperating on California crude from the Los Angeles basin. The wholeprocedure above outlined takes on the average about 1 hours, from thetime the fires are extinguished until the plant is again under normaloperating conditions, whereas, by the former method of cleaning thetubes(by use of a turbine-driven cleaning'device) about five hours isrequired for cooling before the heating coll can be opened for cleaningand about six hours is required for the actual cleaning operation sothat, on the average, the heater is out of service for about elevenhours.

By employing the present method of cleaning at regular intervals of tendays to two weeks, the damaging or burning of tubes from overheating,due to carbon deposits, has been entirely eliminated and practicallycontinuous smooth operation of the process has resulted over periods aslong as three months. Without employing the periodic method of cleaningprovided by the present invention, it was necessary to shut down thefurnace and turbine the tubes at least once a month. It is estimatedthat the method of the present invention has decreased the maintenanceand cleaning costs on this particular furnace installation by at least50% and it is now in regular use in a large number of such furnaces.This 50% decrease in maintenance cost does not take into considerationthe increase in productive operating time obtained when employing theprocess of the present invention, due to the decreased time required forcleanouts, not to mention, from an operation standpoint, the loss intime of this particular furnace while being turbined.

I claim as my invention:

1. In a process for heating hydrocarbon oils by passing the samecontinuously through a fluid conduit within a furnace, the method ofpreventing the excessive accumulation of coke within the conduit whichcomprises periodically discontinuing the supply of heat to the fluidconduit from the furnace and discontinuing the supply of oil to thefluid conduit, removing the oil from the fluid conduit and introducingthereto a mixture of water and steam, continuing the supply of water andsteam to the fluid conduit until the temperature of the materialsdischarged therefrom is below the temperature of saturated steam,further cooling the fluid conduit by the continued passage of watertherethrough, then charging the fluid conduit with hot oil at atemperature of at least 400 to 600 F., then rapidly passing a stream or.relatively cold oil through the heating coil to flush out thecarbonaceous material and subsequently 5 lighting the fires andcontinuing normal operation of the process.

2. A process 'for removing carbonaceous deposits from the fluid conduitof an oil heater embodying the steps which comprise cooling the 10 fluidconduit by passing aqueous fluid therethrough, reheating the fluidconduit by charging the same with hot oil and flushing the fluid conduitwith relatively cold oil.

3. A process for removing carbonaceous de 15 posit from the fluidconduit of an oil heater which comprises passing water and then hot oilthrough the conduit to'loosen the carbonaceous material by resultingcontraction and expansion of the conduit, and then flushing the latter20 out of the conduit.

4. A process for removing carbonaceous deposit from the fluid conduit ofan oil heater which comprises passing steam, water and hot oil throughthe conduit in the order named,

thereby loosening the deposit, and then flushing the loosened materialout of the conduit.

5. A process for removing carbonaceous deposit from the fluid conduit ofan oil heater which comprises passing steam, water, hot oil andrelatively cold oil through the conduit in the order named.

6. A process for removing carbonaceous deposits from the fluid conduitof an oil heater which comprises alternately contracting and expandingthe conduit by alternately passing relatively cold and relatively hotfluids therethrough in the absence of combustion whereby the depositsare loosened and finally flushing the fluid conduit.

7. A process for removing carbonaceous deposits from the fluid conduitof an oil heater which comprises alternately contracting and expandingthe conduit by alternately passing relatively cold and relatively hotliquids therethrough whereby the deposits are loosened and finallyflushing the fluid conduit.

CHARLES L. JOHNSTON.

